The invention relates, in general, to munitions, and, in particular, to test projectiles.
Collateral damage caused by munitions is a problem. There is a need for precision munitions that may reduce collateral damage. This need has been present for years and will continue into the future due to the nature of many modern-day battlefields.
Projectiles may be stabilized in flight by spinning the projectile or by using fins on the projectile. A spin stabilized round or projectile may attain flight stability due to an interference fit between a metallic driving band mechanically attached to the projectile and the lands and grooves (rifling) in the launching tube. The interference between the metallic driving band and the rifling in the tube may also seal the propellant gases behind the driving band. As the projectile travels down the launching tube, the twist of the rifling in the tube may impart rotational motion to the projectile through the band. Thus, the projectile may exit the tube with spin, which may help stabilize the projectile in flight. A spinning projectile may have a spin rate of about 200 hertz or more.
Many of today's precision munitions may be fin stabilized. When shot from cannon, a fin stabilized projectile may seal the propellant gas behind it to produce the pressure needed to propel the projectile out of the cannon tube. A slipped obturator may be used to seal the gas behind the projectile. The slipped obturator may seal propellant gases behind it much like a piston ring in an internal combustion engine. The slipped obturator may be placed near the rear of the projectile. The slipped obturator may cause an interference fit between the rifling in the launching tube and the projectile.
Unlike the metallic driving band, however, the slipped obturator may not be mechanically coupled to the projectile body in the radial direction. As the projectile travels down the launching tube, the rifling may cause the slipped obturator to spin. The interference between the slipped obturator and the tube wall may seal the propellant gases. But, because the projectile is decoupled from the slipped obturator, the projectile may not spin at the same rate as the slipped obturator or induce the magnitude of spin of a metallic driving band. The reduction in spin from the slipped obturator to the projectile may be needed for proper functioning of some guidance and navigation systems that are part of a precision guided munition.
The projectile with the slipped obturator may have a spin rate of about 0 hertz to about 80 hertz, for example. The spin rate of a projectile with a slipped obturator is much less than the spin rate of a projectile with a driving band. As used in the specification and claims, and as known in the art, a “non-spinning” projectile or round with a slipped obturator may have some small amount of spin, but that amount of spin is very much less than the spin of a “spinning” projectile with a driving band.
The guidance and navigation systems in precision munitions may be very expensive. This expense, coupled with the desire to increase the range of precision munitions, has created a need to test projectiles at extreme loads. The same statistical inference may be obtained at a lower cost by testing a projectile a fewer number of times, near the upper bounds of its operating conditions (i.e., Permissible Maximum Pressure (PMP)+25% above normal), than by testing a projectile a greater number of times, at only a small amount above its normal operating conditions (i.e., PMP+5% above normal).
The guidance and navigation systems of a projectile may need to be tested at the upper bounds of a projectile's operating conditions. Also, it is necessary to determine if the failure may occur at gun launch or at projectile impact. Methods of catching a projectile that stop the projectile's forward movement without damaging the projectile are known. These “soft catch” methods include the rail gun and the soft catch recovery system along with shooting into impact areas amenable to the preservation of the projectile. The rail gun simply shoots the projectile into a closed rail system that has a water medium to slow the projectile down. The soft catch recovery system goes one step further and uses a mass/spring damper of air and water in series to better control deceleration of the projectile. The soft catch recovery system may produce more accurate data with less balloting of the projectile and a slower de-acceleration rate.